1. Field of the Invention
This invention is directed to a frequency multiplier capable of operating on a wide frequency range, and the practical application thereof to the generation of timing signals.
The wideband frequency multipliers in accordance with the invention is particularly necessary in data media reading devices wherein the reading operation requires a relative motion between the medium and the reading unit. These media are, generally, comprised of the data to be read as well as regularly-spaced marks intended to ensure the synchronization of the reading circuit operation with respect to the motion. The data reading units, or special units, read these marks and, from the periodic signal resulting from this reading operation, a frequency multiplier produces a timing signal the time-period of which is a submultiple of the periodic signal. The timing signal controls the various operating steps involved in the reading operation. Since the relative motion speed is varied, the time-period which is to be divided by the frequency multiplier will consequently be varied. This variation is of particular concern in applications where the data media is moved manually such as a badge reader. For example, in reading a badge, this speed may vary between about ten centimeters per second and more than one meter per second.
In such applications, it is apparent that the frequency multipliers based on the selection of the harmonics of a non-linear amplifier, cannot be efficiently utilized, if at all. When the speed variations are limited, as in magnetic tape drives, for example, systems may be used which are based on the synchronization of an oscillator by the signals resulting from the reading of magnetically recorded marks and/or data. The frequency variation range of an oscillator, however, is relatively quite limited. Thus, in the above-mentioned application of the reading of a badge, such a method or technique cannot be employed.
The frequency multiplier in accordance with the invention does not require any tuned circuit such as an oscillator requires. Nor does the frequency multiplier in accordance with the invention require a filter. Therefore, the frequency multiplier in accordance with the invention may operate on a very wide frequency range. It is based on a time measuring technique wherein a linearly varying voltage is compared with a reference voltage.
2. Description of the Prior Art
Reference is made to U.S. Pat. No. 3,585,502, entitled "Method and Apparatus for Subperiod Measurement of Successive Variable Time Periods" granted June 15, 1971 to Joseph W. Baker on application Ser. No. 749,142, filed July 31, 1968.
U.S. Pat. No. 3,585,502 is directed to a self-clocking method and apparatus for continuously detecting desired subperiods of time periods between successive pulses where the time periods may vary. The successive pulses indicate the start and stop of each time period. A switching network responds to the start-stop indications to generate a responsive signal, e.g., a ramp function signal. The characteristics of the ramp are dependent upon the start and stop indications. A comparator network compares the magnitude of the responsive signal to a reference signal stored from the preceding period.
Reference is made to U.S. Pat. No. 3,548,317, entitled "Time Division Frequency Multiplier" granted Dec. 15, 1970 to Michael P. Bordonaro on application Ser. No. 645,267, filed June 12, 1967.
U.S. Pat. No. 3,548,317 is directed to a frequency multiplier with an input frequency which is variable over one decade and in which input pulses reset a linear ramp voltage to a negative voltage level from which a ramp voltage increases to a positive level. The ramp voltage is applied to a zero crossing detector which changes state each time the ramp voltage crosses the zero voltage level. Each time the zero crossing detector changes state, an output pulse is provided at the output terminal. There are two such output pulses for each input pulse since the ramp voltage crosses zero during resetting of the ramp generator and as the ramp voltage builds up from its initial value.
Reference is made to U.S. Pat. No. 3,548,318, entitled "Ramp Function Generator", granted Dec. 15, 1970 to Daniel S. Yorksie, on application Ser. No. 755,857, filed Aug. 28, 1968.
U.S. Pat. No. 3,548,318 discloses a ramp function generator for providing a symmetrical saw-tooth voltage waveform in response to a square wave oscillator of the type having first and second switching devices which are alternately conductive. The ramp function generator includes first, second and third capacitors. The generator provides a saw-tooth voltage waveform having a frequency equal to twice that of the square wave oscillator, and synchronized therewith.
Reference is made to U.S. Pat. No. 3,970,828, entitled "System for Precision Time Measurement" granted July 20, 1976 to Albert M. Klein on application Ser. No. 540,332, filed Jan. 13, 1975.
The ABSTRACT of U.S. Pat. No. 3,970,828 reads as follows:
"A system for measuring a first period of time, for example a period between a pair of pulses, with an extraordinarily high degree of accuracy. Two ramp voltages of different slopes are started in synchronism with the first occurring pulse. The ramp with the largest slope is then sampled and held on receipt of the second occurring pulse. A counter counts a clock of a moderate pulse repetition frequency (PRF) during a second period occurring between the time the ramps are started and the time the amplitude of the ramp of the smaller slope becomes equal to the sampled amplitude of the ramp of the larger slope. The count stored in the counter at the end of the second period is then directly proportional to the first period or is equal thereto. Moreover, the count can be far more precise than it would be by counting the clock PRF during the first period. By making the larger ramp slope 1,000 times as large, for example, as the smaller ramp slope, the precision of the measurement may be increased 1,000 times for the same clock PRF." PA1 a sawtooth signal generator produces a linearly varying periodic voltage the frequency of which is equal to the frequency to be multiplied; a storage device stores the maximum of this voltage or a value closely approaching the maximum; a voltage divider provided with a number of taps, each tap being associated with a comparator, each comparator compares the voltage value at its associated tap with the instantaneous voltage value of the sawtooth voltage and produces a signal when comparison occurs; logic devices combine these signals in order to form a periodic signal the frequency of which is a multiple of that of the input signal.